Over 2500 Gold Coins with a combined weight of almost 20 KG found during construction in Germany, 1993.
Note the paltry payoff given to the man who recovered the bulk of the treasure - a mere 20, 000 DM. No wonder the vast majority of ancient treasures get melted down - the law actively discourages the finding of treasure.
This was the largest Roman Era gold hoard ever discovered.
Regardless of the gold value, the historical value is priceless, and this is precisely what is lost when things go onto the black market.
Link: Wikipedia on Trier Gold Hoard